The present invention relates to a light source device for use in an image forming apparatus and using a semiconductor laser.
A digital copier, laser printer, facsimile apparatus or similar image forming apparatus extensively used today includes a light source device having a semiconductor laser and a collimator lens. Optical characteristics required of the light source device include the directivity of laser light (optical axis characteristic) and the parallelism of a beam (collimation characteristic). To meet these requirements, it is a common practice to adjust the relative position of the emission point of the laser and the collimator lens in the directions of three axes (x, y and z). The positional accuracy is severely restricted to below the order of microns. Therefore, the device using the laser and collimator lens must be capable of being adjusted in the thee axis directions and then fixed at its adjusted position.
When the collimator lens is fixed in place by adhesive, the adhesive contracts in the event of setting. It is therefore necessary to reduce the influence of the contraction on the optical characteristics as far as possible. Particularly, high accuracy is required of the device in the direction z (optical axis direction), so that the contraction should preferably be prevented from occurring in the direction z. For this purpose, the adhesive layer should preferably extend substantially parallel to the optical axis (axis z). Also, the contraction should preferably be limited to one of the directions x and y in order to facilitate adjustment even in such a direction.
Light source devices each having a semiconductor laser and a collimator lens are taught in, e.g., Japanese Patent Laid-Open Publication Nos. 5-88061, 5-136952, and 5-273483. However, the conventional devices of the type described have some problems yet to be solved, as follows:
(1) Each device needs a number of constituent parts which increase the cost.
(2) The constituent parts are dislocated in the directions x, y and z in the event of assembly, so that the directivity (optical axis characteristic) of the laser is deteriorated.
(3) Use cannot be made of ultraviolet light curable adhesive for fixing the collimator lens in place. This kind of adhesive can set in a short period of time in a desired manner and is highly reliable.
The conventional devices have other problems which will be described, in addition to the above problems.